Contemporary remote demolition robots using hydraulic tools sometimes experience a problem when the hydraulic pressure of a tool differs from the hydraulic pressure of other actuators, such as arms or booms. A load sensing hydraulic system functions in such a way that the flow of the hydraulic fluid supplied by one (or more) pump(s) is shared between more than one actuator, an actuator in this application meaning a hydraulic motor or cylinder for operating a robot member such as an arm, a boom, a tool, a tool holder or a hand to mention a few examples. With reference to FIG. 1, such actuators may be the cylinders 12 for operating the arms 11, or with reference to FIG. 3, the motor (not shown explicitly) for operating a power saw or a rotating drum cutter 11b being two examples of a tool.
When a saw or rotating drum cutter (hereafter simply referred to as a cutter) is first activated it revs up, bringing for example the saw blade to rotate at a very high revolution speed. When this is done, the saw blade or cutter is most likely not in contact with the material to be cut and the revving up can thus be performed at a very low pressure.
Load sensing hydraulic systems operate in such a manner that the flow generated by one pump is shared among more than one actuator. If one actuator is operating at a low pressure and another actuator is operating at a high pressure and when the pump is operating to provide full flow, all or most of the fluid will flow in the direction presenting the least pressure. The situation may thus occur that the arms are operated to move the cutter in to close vicinity of for example a wall and then as the cutter or saw is revved up, which happens at low pressure, the fluid will redirect itself to the tool, leaving the arms unworkable, the cylinders for the arms presenting a much higher working pressure. The arms will thus not be operable and the tool can not be moved while operating freely.
To overcome this, the prior art provides for using a proportional hydraulic valve. Such a valve does not open fully and only allows a portion of the flow to pass through, for example 75-80%, leaving the remaining 20-25% of fluid flow to flow to other actuators. In such a manner the flow is shared between different actuators.
However, such a proportional valve, actively throttling the flow, generates an energy loss which is dissipated in the form of heat. Not only does this reduce the amount of power that is available from what is delivered by the pump by approximately 1.2 kW in an example where the available power is 18 kW, the reduction thus representing a fair share of the available power, but it also increases the temperature of the hydraulic fluid which leads to a decreased lubrication which can, in turn, decrease the longevity or lifespan of some components.
There is thus a need for a remote controlled demolition robot that is able to operate fully irrespective of what function is undertaken even when flow is shared between several actuators.